1. Field of the Invention
The invention relates to an adjustable prosthetic leg, and more particularly to an adjustable prosthetic leg that allows a user to climb up or go down the stairs or walk on uneven ground easily without losing balance.
2. Description of the Related Art
For those who experience amputation due to serious trauma or lesion or for those having congenital limb deficiencies, through the reconstruction of a prosthetic limb, appearance and functions that are comparable to those of a common person can be attained. Especially for those who lose the leg below the knee, besides an essential artificial foot, what's most important is a prosthetic leg connecting the thigh and the artificial foot.
Referring to FIG. 1A or FIG. 1B, a conventional prosthetic leg, which is connected between a thigh 1a and an artificial foot 2a, generally comprises a controller 3a, a connecting mechanism 4a, and a knee joint body 5a. The controller 3a is connected to the thigh 1a. One end of the connecting mechanism 4a is pivotally connected to the controller 3a, and the other end is pivotally connected to a piston structure 51a inside the knee joint body 5a. Furthermore, the controller 3a is also pivotally connected to the knee joint body 5a. 
The knee joint body 5a has a hydraulic cylinder 50a provided therein. The piston structure 51a is provided inside the hydraulic cylinder 50a. The connecting mechanism 4a is connected to the piston structure 51a. The piston structure 51a divides the hydraulic cylinder 50a into an upper hydraulic compartment 52a and a lower hydraulic compartment 53a. In addition, a flow path 54a is provided inside the knee joint body 5a for connecting the upper hydraulic compartment 52a and the lower hydraulic compartment 53a. Thus, when the connecting mechanism 4a drives the piston structure 51a to move up and down, the volumes of the upper hydraulic compartment 52a and the lower hydraulic compartment 53a are changed. In addition, a change in the volumes of the upper hydraulic compartment 52a and the lower hydraulic compartment 53a may also exert an influence on the movement of the connecting mechanism, thereby further affecting the bending of the prosthetic leg.
Referring to FIG. 1A, when a user intends to lift the thigh 1a to take a first step, the crus and the knee joint body 5a droop naturally under the action of gravity. In such a case, the connecting mechanism 4a stretches and pushes the piston structure 51a to move downwards, the volume of the lower hydraulic compartment 53a is compressed, and a hydraulic liquid in the lower hydraulic compartment 53a is injected into the upper hydraulic compartment 52a through the flow path 54a. At this time, the artificial foot 2a does not touch the ground, and thus is not affected by a reactive force; therefore, the knee joint body 5a can rotate freely along with the thigh 1a. 
Referring to FIG. 1B, when the user steps on the ground with the artificial foot 2a, the thigh 1a applies a force for stretching so that the relative position between the thigh 1a and the artificial foot 2a changes from being bent to being stretched, and the connecting mechanism 4a is bent and drives the piston structure 51a to move upwards. In this case, the volume of the lower hydraulic compartment 53a increases, and the volume of the upper hydraulic compartment 52a decreases. It should be particularly noted that the center of gravity of the user is inevitably located on this foot at this time, so that the knee joint body 5a cannot swing along with the thigh 1a; otherwise, the user may fall down. The reactive force applied on the artificial foot 2a by the ground contributes to this effect, because the reactive force may be transferred to the piston structure 51a, such that the piston structure 51a is fixed at a position until the artificial foot 2a leaves the ground again and the gravity center of the user is moved to the other foot.
However, what is described above is the situation of walking on even ground. In the case of climbing up or going down the stairs or walking on uneven ground, it is required that the body weight can be supported before the thigh 1a and the artificial foot 2a are stretched in a straight line. That is, a mechanism is required through which the volumes of the hydraulic liquid in the upper hydraulic compartment 52a and the lower hydraulic compartment 53a remain the same when the prosthetic leg is bent. Otherwise, the user may lose balance and fall down. To overcome this difficulty, many advanced prosthetic legs get available on the market, for example, Taiwan Patent Publication No. 564742 and EU Patent Publication No. 2478875. However, the former, due to design mistakes, cannot practically fully satisfy the requirements of a user for climbing up or going down the stairs and walking on uneven ground. The latter depends on a large amount of electronic sensing devices, which increase the cost; and the electronic elements are of low reliability and are not water-proof, which fails to meet the requirements of the industry and the users for prosthetic legs.
Therefore, in response to the requirement for improvement of the above shortcomings, the present invention which is reasonably designed and overcomes the above shortcomings is made by the inventor through intense research and application of academic principles.